Polling stations have closed in Senegal after a day of voting that passed largely without incident.
Ballot counting has started across the country with results being announced over public and private radio stations.
Macky Sall and Idrissa Seck are the main opposition challengers and most observers expect one of these candidates to face the incumbent Abdoulaye Wade in a second round run-off.
Foreign diplomats had earlier this week issued appeals for a calm and transparent vote.
"We are closely watching the development of the situation. I have been concerned about what is happening there," Ban Ki-moon, the UN secretary-general, told journalists when asked about Senegal during a visit to Zambia on Saturday.
Apart from some polling stations opening late, voting appeared to take place smoothly, according to a national network of observers.
"We are seeing a good turnout. There have been practically no incidents. Things are calm," said Abdou El Mazide Ndiaye, head of an election "situation room" set up by the RESOCIT network of national observers.
Senegal, a former French colony, is one of the continent's pioneer democracies, boasting an unbroken series of elections since independence in 1960.
Yet Wade's third-term bid has proved a test of Senegal's democratic credentials, prompting international concern and weeks of protests.
Hundreds of voters booed Wade, 85, as he cast his ballot. The incumbent, accompanied by his daughter Sindiely and son Karim, arrived just after midday at the polling station in the suburb of Point E where long lines of voters had been waiting for hours in the sun.
Several dozen supporters applauded his arrival, but their appreciation was drowned out by a cacophony of boos and jeers.
Visibly angry, a tense Wade pushed one of bodyguards out of the way as he left. He beat a swift retreat after casting his ballot and did not speak to reporters.
Despite having served two terms in office, a limit he himself introduced, Wade says 2008 constitutional changes extending term lengths to seven years allow him to serve two more mandates.
The second-oldest African leader after Zimbabwe's Robert Mugabe, 88, Wade says he needs more time in office to finish his "grand projects".
The voting started after a proposal on Saturday night by Olusegun Obasanjo, the African Union envoy, suggesting Wade retire in two years if he is re-elected, seeking to ease tensions the night before the polls.
Amsatou Sow Sidibe, one of two female candidates in the election, said the situation in Senegal was too complex to be solved by his proposal.
"There are a range of reforms needed in this country, but how can you wait until the eve of an election to come and make proposals that suggest that if Wade wins the election, he could stay for two years?" she said.
"I think that is totally illegal. We totally disagree with Obasanjo's proposals."
Sidibe said delaying the election was out of the question, adding that it was repeated election postponements that led to the standoff in Ivory Coast.
"In Africa, when ever you delay an election, you are asking for trouble," Sidibe said.
|President Abdoulaye Wade's contentious bid for a third term sparked deadly protests in the country [EPA]
The June 23 Movement, an alliance of opposition parties and activists, called for a presidential election to be organised within six to nine months, one in which Wade does not take part.
Wade was in the opposition for 25 years before unseating the Socialist Party in 2000. He has remained defiant in the face of the storm of criticism at home and abroad.
He has dismissed opposition protests as "temper tantrums" and heaped derision on calls from France and the US that he retire.
He would not be dictated to by "Toubabs", he said, using the Wolof term for Westerners.
Senegal's music icon and political activist Youssou N'Dour has called for change in the country, warning that its citizens would not accept an "electoral coup".
The Grammy-winning singer whose own ambitions to run in the election were rejected by the country's highest court, voted in the suburb of Mermoz, walking with a slight limp after being injured during a protest.
"What counts, what is important to the Senegalese, is change. Real change," N'Dour said. "We will not accept an electoral coup ... the Senegalese will not accept that these elections be sullied."
Senegal is a nation of 13 million. Its biggest industries are fishing, tourism and groundnut production, but a large proportion of Senegalese live in poverty.
Those who support Wade point to considerable infrastructure development under his governance.
His opponents argue that his focus on grand legacy projects has left him out of touch with the concerns of the average citizen.
An estimated 5.3 million people were registered to vote in Sunday's election.
With reporting from Azad Essa in Dakar. Follow him on Twitter at @azadessa